Complex Call with Different Messages in Bokermannohyla ibitiguara (Anura, Hylidae), a Gladiator Frog of the Brazilian Cerrado
The Gladiator Frog, Bokermannohyla ibitiguara, is a hylid endemic to the Brazilian Cerrado with a complex call composed of long and short notes. We describe the influence of male size and temperature on call properties and investigate the social contexts of the different notes of the call through direct observations and playback experiments conducted in the field. The dominant frequency correlated negatively with male body size, whereas the duration of the long note correlated positively; there was no correlation between pulse rate and male body size. Air temperature correlated negatively with the duration of the long note and positively with pulse rate. Playback experiments with males indicated that they did not change the proportion of long to short notes in the presence of an intruder (= playback), but rather, they changed the short notes, which became longer, with a lower dominant frequency and more pulses with variable intervals. We interpreted this call as an aggressive call. Our results suggest that females may choose males based on dominant frequency and duration of the long note, traits that might be under sexual selection. Moreover, short notes appear to be the territorial component of the mixed call, and the aggressive call is a variation of this component.
Bokermannohyla ibitiguara é um hilídeo endêmico do Cerrado brasileiro que possui um canto complexo, composto de notas longas e curtas. Neste estudo, descrevemos a influência do tamanho do macho e da temperatura do ar nas propriedades acústicas do canto, investigando também os contextos sociais das diferentes notas através de observações diretas e experimentos de playback conduzidos no campo. O tamanho do macho correlacionou-se negativamente com frequência dominante do canto e positivamente com duração da nota longa; não houve correlação com taxa de pulsos. A temperatura do ar correlacionou-se negativamente com duração da nota longa e positivamente com a taxa de pulsos. Os experimentos de playback mostraram que machos não alteram a proporção de emissão de notas curtas e longas na presença de um intruso (= playback); ao invés disso, machos modificam as notas curtas, tornando-as mais longas, com frequência dominante mais baixa e com mais pulsos com intervalos variáveis. Nós interpretamos tal canto como sendo o canto agressivo. Nossos resultados sugerem que, potencialmente, as fêmeas podem escolher os machos avaliando a frequência dominante do canto e a duração da nota longa, características que podem estar sob seleção sexual. Além disso, as notas curtas parecem ser o componente territorial do canto misto, sendo o canto agressivo uma variação de tal componente.Abstract
Resumo
Location of Brazil in South America; in detail, our study site (star) in the Cerrado of Minas Gerais state (MG), southeastern Brazil.
Regression analyses between acoustic parameters of the advertisement call and male body size in Bokermannohyla ibitiguara, municipality of Sacramento, Minas Gerais, Brazil. A and B: 49 males; C and D: 40 males.
Regression analyses between temporal acoustic parameters of the advertisement call of Bokermannohyla ibitiguara and air temperature, municipality of Sacramento, Minas Gerais, Brazil. A: 40 males; B: 38 males.
Mean number of notes (vertical axis) emitted by males before and during each playback (PB) treatment (T1, T2, T3). The * indicates significant statistic differences (P < 0.05). Gray bars = long notes; white bars = short notes (see text for details).
(A) Two short notes commonly emitted by Bokermannohyla ibitiguara males under natural conditions and (B) two short aggressive notes emitted during playback. Oscillogram above and spectrogram below. In B, notes appear to be more intense and composed of separate groups of pulses with variable intervals, whereas in A, notes are composed of one group of short pulses.
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